A) Field of the Invention
The present invention relates to an optical disc recording method and apparatus of a mark length recording type for recording information in an optical disc by radiating a laser beam to the record surface of the disc and forming pits, and to technologies of improving the quality of a signal recorded at a 16× write-speed or higher.
B) Description of the Related Art
The CD Write Once (CD-WO) standards (generally called the Orange Book standards) are known as one recording method for recordable optical discs. According to the CD-WO standards, information is recorded in an optical disc as a combination of pit and land (between pits) having a length of 3T to 11T (at 1×, 1T= 1/4.3218 MHz=231 ns, at 2×, 1T is ½ of the length at 1×, at 4×, 1T is ¼ of the length at 1×, at 6×, 1T is ⅙ of the length at 1×, . . . ). As shown in FIG. 2, the power of a recording laser beam for a CD-WO disc (generally called a CD-R disc) is set to a recordable top power (record power) in a pit forming area and to a reproducible and unrecordable bottom power (reproduction power) in a land forming area. If a pit is formed by applying the top power during the period corresponding the pit length, the formed pit has a length longer by about 1T because of remaining heat of the laser beam. To avoid this, according to the conventional record strategy, the continuation period of the top power is controlled to be set to (n−K)T for each pit length nT, where n=3, 4, . . . , 11 and K is a constant. The value of the constant K was given by the approximate equation (refer to JP-A-2000-11382):K=−0.16×+1.2 for cyanine disc; andK=−0.15×+1.15 for phthalocyanine discwhere× is a write-speed.
According to this approximate equation for the K value, the K value decreases as the write-speed increases, and the sign of the K value becomes negative at about the 8× write-speed. The K value at the 16× write-speed is −1.36 for a cyanine disc and −1.25 for a phthalocyanine disc. Experiments made by the inventor have demonstrated, however, that 16× recording at this K value makes the continuation period of the top power still too long and the write signal quality is lowered (large jitter and high error rate).